The detection of microorganisms in body fluids, particularly bacteria in blood, requires that a sample of the fluid be used to inoculate a liquid nutrient medium. Subsequently, the liquid medium is in turn used to inoculate a solid medium to continue the growth of the organisms and to make them visible to the naked eye as colonies.
Normal monophasic systems consist of a liquid medium in a culture bottle or vial which is inoculated with a sample of the fluid and is then incubated for a desired period of time (24-48 hours). After that, a sample is withdrawn from the bottle and is used to inoculate a solid nutrient medium (e.g. agar in a Petri dish). This procedure is laborious, sometimes hazardous and includes the risk of contamination with microorganisms from the environment. Additionally, the atmosphere above the liquid medium and surrounding the solid media is contaminated with ambient air when the solid media is inoculated. This is undesirable when the microorganism requires an anaerobic environment.
Detection systems have been developed in which liquid and solid culture media are combined in the same container. Such systems avoid the troublesome and sometimes hazardous transfer of the liquid culture to the solid culture medium. U.S. Pat. No. 2,992,974 to Belcove et al, for example, describes a biological testing device in which a solid medium is restrained in the top portion of a rectangular culture bottle while a liquid nutrient medium is provided in the lower most portion of the bottle. U.S. Pat. No. 3,589,983 to Holderith et al describes a culture bottle which is designed to hold a solid agar nutrient material at a location along the axial centerline of a bottle. The bottle also houses a liquid nutrient broth which may be separated from the solid agar by positioning the bottle on its side.
The above described devices which combine a liquid nutrient medium in a single container with a solid medium have a major disadvantage in that the culture assembly must be positioned in a certain manner prior to contacting the solid medium with the precultured liquid medium. The above described devices for separating solid and liquid culture media are complicated and facilitate separation of the liquid media and the solid media only during incubation, but not during transport. These constructions are not suitable for assembly at the point of manufacture because contact between the liquid and solid media during shipping and storage prior to use causes constituents in the solid medium to elute into the liquid medium.
U.S. Pat. No. 4,308,347 to Forrer et al. describes a device for detection of microorganisms in a fluid sample which includes a first container holding a liquid nutrient medium and a second container containing one or more solid nutrient medium. The containers are detachably connected so that the media can be brought into contact when desired. The device described in the Forrer et al. patent is complicated and requires several manipulative steps to bring the precultured liquid media into contact with the solid medium.
A culture bottle assembly for the detection of microorganisms in body fluids is described in U.S. Ser. No. 056,518, filed June 1, 1987 by Hammann. The Hammann culture bottle assembly comprises a single container divided into a first lower compartment and a second upper compartment by a flange on the interior of the container. A frame is provided for insertion into the second upper compartment. The frame has a lower peripheral edge which can be lowered into mating relationship with the flange. A resilient material is disposed on the lower peripheral edge. Closure means are provided which cause the frame to move downwardly and compress the resilient material against the flange to close the container and to seal the two compartments from each other. The first lower compartment contains a liquid nutrient medium and the second upper compartment contains one or more solid media. A fluid conduit is provided through the frame whereby a specimen can be inserted through an aperture in the closure means into the fluid medium in the lower compartment. After a sample is incubated in the liquid medium for a desired period of time the closure means are moved to a second position which provides an open space above the internal flange through which the precultured liquid medium can be transferred into contact with the solid media when the container is turned over. The culture bottle assembly described by Hammann is a vast improvement over earlier devices, but the possibility exists that a person loosening the closure to axially move the frame could turn the closure too far allowing fluid to leak out of the container when the assembly is inverted.